Conventional large diameter circular knitting machines are normally provided with a set of segmental cylinder knitting cam support blocks surrounding the needle cylinder of a given diameter, and a set of segmental dial knitting cam support blocks positioned on the dial for actuating the respective cylinder and dial needles at each yarn feeder. A plurality of yarn feeders and knitting cam segments are provided on each of the segmental knitting cam support blocks and spaced from each other so as to comprise an annular body. The number of yarn feeders in a circular knitting machine increases or decreases according to the diameter of the needle cylinder and the dial and the number of setting positions of the feeders also increases and decreases. The number of yarn feeders to be used with a needle cylinder of a given diameter is normally determined by equally dividing the circumference of the annular body by the space required for one yarn feeder to determine the width to be occupied by each arcuate part of each segment of the annular body and then making adjustments in widths of the segments to provide for increases or decreases in the number of yarn feeders. Thus, the number of segmental knitting cam support blocks required is determined by the given diameter of the needle cylinder to be employed. For example, in a circular knitting machine with a needle cylinder of 20 inches in diameter and with 41 yarn feeders, the annular body is first equally divided into 41 spaces. Then, if four feeders are to be carried by one segmental knitting cam support block, the annular body is divided into 10 segments, and the remaining one feeder [41-(4.times.10)=1]is provided on one of the segmental knitting cam support blocks. When the circular knitting machine has a needle cylinder of 19 inches in diameter and with 39 yarn feeders, the annular body is first divided into nine segments and the remaining three feeders [39-(4.times.9)=3]are supported on certain of the segmental knitting cam support blocks. Accordingly, the yarn feeders are equally supported on respective segmental knitting cam support blocks while any remaining yarn feeders are supported on other segmental knitting cam support blocks which are different in widthwise dimensions from the equally divided segmental knitting cam support blocks.
In accordance with this conventional arrangement, circular knitting machines of the same kind, but having needle cylinders of different size, are manufactured and a manufacturer of tubular knitted fabric must have circular knitting machines in the mill which are of various nominal sizes (diameters) in order to produce tubular fabric of different given diameters. If it were possible to easily convert a given size of knitting machine to permit a limited range of needle cylinders of different diameters to be used on a given circular knitting machine, the number of knitting machines required by the knitting fabric manufacturer could be reduced and many advantages could be offered to the management of knitting machines and to economy. For this purpose, the size or diameter of the knitting machine could be changed by reducing the number of replacement parts to be applied to the knitting machine by the common use of setting positions of segmental knitting cam support blocks to be replaced.